1. Field
The present disclosure pertains to a method and a system for detecting expiratory flow limitation (EFL) by controlling pressure to a subject's airway.
2. Description of the Related Art
Chronic obstructive pulmonary disease (COPD) is a major public health problem. It is the fourth leading cause of chronic morbidity and mortality in the United States, affecting over 24 million Americans. It is the third leading cause of death in the United States after heart disease and cancer, and by the 2020s it is projected to be the third leading cause of death worldwide. The increased mortality is driven by the expanding epidemic of smoking and the aging population worldwide.
COPD is an umbrella term used to describe progressive lung diseases including emphysema, chronic bronchitis, non-reversible asthma, and some forms of bronchiectasis. COPD is characterized by increasing breathlessness. Patients with COPD may have difficulty exhaling because of the deterioration of their lung tissue or the inflammation of their airway walls. This condition is commonly referred to as Expiratory Flow Limitation (EFL). EFL seriously affects the quality of life and can ultimately contribute to acute respiratory failure.
Common treatments for EFL are Positive end expiratory pressure, PEEP, and/or pharmaceuticals. The level of PEEP to be applied to a patient is generally determined in a more or less arbitrary fashion.
With patients in the ICU, EFL is typically detected with a manual maneuver that is externally applied to the patient's body. For example, a clinician or respiratory therapist typically exerts force on the patient's abdomen at the onset of exhalation. This force causes an increase in the pressure difference between the lungs and mouth that should drive the exhalation flow. If the patient has EFL, the exhalation flow does not increase. This technique, however, is not applicable for a chronic patient at home.
Other techniques for the detection of EFL are the ΔXrs with forced oscillation technique (FOT) and the negative expiratory pressure (NEP) method. Such methods are available as stand-alone devices or as part of multifunctional spirometers. These techniques are typically used for non-ventilated patients. The NEP method is conceptually similar to the application of pressure on the abdomen. It replaces the increasing pressure in the lungs from abdominal compression with negative pressure applied at the mouth. The ΔXrs with FOT method relies on the change in the reactance of the respiratory system when EFL occurs. In order to “measure” the reactance, a forced sinusoidal pressure signal is applied.